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stevefh

compression S4 1993.5 turbo

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Hi all   My compressions are  140,100,100,140 approx.I know 140 is the minimum but what is a good /max compression figure?

I use little oil and its not milky.Does this imply its not the rings?

No excess water or smoke coming out of the exhaust.Does this imply its not the  head gasket?

I think I have poor mpg.

Valve clearances done 28,600 miles ago.

I think I understand the leak down test and what the results mean concerning the valves leaking or not,but I wont know the cause.Do you know how to make a decision?

How do I know before I start the job if its the  valve clearances as opposed to the nightmare of engine/gearbox out to do a de-coke.Thanks for any help.

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I assume that's a dry test? If you put a tablespoon of oil in each cylinder and test again that you can see if it's valves or rings with the difference in the results. If the compressions are much higher, it's the rings - if only a tiny bit higher, it's the valves.

 

http://www.gregsengine.com/cylinder-compression-testing.html

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Compressions should be within 10% of each other, there's something amiss on 2 & 3... 

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What do the plugs look like on 2&3  and can you see any oil if you shine a light down the plug thread at tdc.

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Was the compression tested on a fully warm engine, and with the throttle held fully open?  If not, then the test was no valid.

 

A leak down test will tell you if the rings or valves are leaking.

 

If the valve clearances have not been adjusted for the recommended miles, or are out of spec, then you should do the measurement, and when the cam towers are removed, then you should to the leakdown test that that time, (popping the valves to clean the seats of debris) to see if the results improve.  It is possible for the carbon buildup to prevent the valves from sealing totally during the compression or leakdown test.

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Thanks for advice given      Does "popping" the valves mean hitting the end of the valve stem with a hammer? Is there no way of knowing, before I start,if its adjusting the shims or a de-coke?Should an S4 need a de-coke after approx.76000 miles of mostly short trips?

My thinking is that valve gear wear would not hold a valve open but rather it would close "early".  Would this happening to the inlet or exhaust valve cause  compression to drop to 100psi? I know 140psi is a minimum but what is a good compression for an S4?

Is there a chemical treatment that will remove carbon deposits from the valve heads and their stems?

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yes, gently hitting the valve spring end with a plastic or rubber mallet to pop the valve off the seat (with cam tower removed).

 

A leakdown test is the method to tell the condition of the valve seats and the rings before taking the engine apart, but there is a chance that crud on the valve will give a poor result.

 

BMW and AUDI will walnut shell blast their valves (through the partially disassembled intake manifold ports) to remove carbon deposits from their direct injection engines... while the engine is mostly assembled...  But I don't think I would do that to an Esprit...

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Thanks for advice given     

My thinking is that valve gear wear would not hold a valve open but rather it would close "early". 

Valve wear occurs when the valve head hammers itself into the seat so closing (reducing) the gap between the can lobe & the follower which can result in the valve leaking in extreme cases.

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